Barrier coated nylon film



y 6, 1970 D. G. JAMES 3,514,367

BARRIER COATED NYLON FILM Filed Aug. 16, 1966 3 SheetsSheet 1 l l/I/I/II I I I I FIG. 2.

I I I I 1 I I I I III FIG. I.

INVENTOR.

DANIEL G. JAMES AGENT May 26, 1970 D. G. JAMES BARRIER COATED NYLON FILM3 Sheets-Sheet 2 Filed Aug. 16, 1966 m mm a n v Q: 5 5 3 mg a o 5 a T 45' m A 3 a a D o .3 I a o 5 5 3 Q lrllq Q Q Q rl l o- 5 I' l HI I -lr MQQ E o a a 3 5 Q a 3 3 5 G 3 2 3 i A1 41A a 5 2 IL a QQ -MQ May 26, 1970o. 6. JAMES 3, ,367

BARRIER COATED NYLON FILM Filed Aug. 16, 1966 3 Sheets-Sheet 3 INVENTOR.

: DANIEL 6. JAMES AGE/VT United States Patent 3,514,367 BARRIER COATEDNYLON FILM Daniel G. James, Chester, N.J., assiguor to Allied ChemicalCorporation, New York, N.Y., a corporation of New York Filed Aug. 16,1966, Ser. No. 572,796 Int. Cl. B44d 1/16; B32b 27/34 US. Cl. 161-165 14Claims ABSTRACT OF THE DISCLOSURE A process for coating nylon film witha polyurethane primer coating, a waterproof coating and a barriercoating, and an article produced by the process. The coated film may belaminated to polyethylene film.

This application relates to novel coated nylon films and to novelprocesses for the production thereof, and particularly to barrier coatedfilms and processes for their production, the terminology barrier coatedfilm being used herein to denote a substrate film to which has beenapplied a coating which is a barrier to (i.e., is relatively impermeableto) oxygen.

Barrier coated films are particularly useful in the food packagingindustry for packaging such products as lunch meats and cheeses due tothe long product shelf life which they provide. In addition to very lowoxygen permeability, such films must be easily thermoformable, of such adegree of transparency and gloss as to give an eye-appealing view of theproduct wrapped therein, and the various coatings comprising the filmmust not separate from each other. Furthermore, the films must be ofsuch a character so as not to impart either odor or taste to theproducts wrapped therein.

The novel barrier coated films which I have discovered possess the aboveproperties and comprise broadly a nylon substrate film, a polyurethaneprimer coating and a barrier coating of a copolymer of vinylidenechloride with one or more of the following comonomers:

methacrylic acid and its alkyl esters, acrylic acid and its alkylesters, acrylonitrile, methacrylonitrile, vinyl chloride, and itaconicacid.

the vinylidene chloride being present in the amount of about 88% toabout 96% by weight. With respect to the alkyl esters of methacrylic andacrylic acid, those esters in which the alkyl group has from 1 to 8carbon atoms have been found to be most suitable, i.e. methyl, ethyl,propyl, butyl, pentyl, hexyl, heptyl and octyl methacrylate andacrylate.

The nylon substrate film used in my novel films can range from about /2to about 5 mils in thickness, preferably about /2 to 2 mils. Thepolyurethane primer coating is the reaction product of a polyestercomponent and a diisocyanate component and is deposited from solution inan organic solvent such as acetone, toluene or ethyl acetate or mixturethereof. The primer coating can range from about 0.005 to about 0.05 milthickness, preferably about 0.01 to about 0.02 mil. The barrier coatingis preferably from about 90 to about 95% by weight vinylidene chloride,can be from about 0.08 to about 0.32 mil thick, preferably about 0.08 toabout 0.16 mil, and is deposited from a dispersion in water.

The novel process which I have discovered for making the above-describedfilm comprises broadly the steps of:

(1) Gravure roll coating a nylon substrate film with a solution ofpolyurethane primer in an organic solvent,

(2) Removing organic solvent from the primer-coated substrate film,

(3) Metering bar coating the primer-coated substrate film with a barriercoating of a copolymer of vinylidene chloride dispersed in water, thecopolymer containing about 88% to about 96% by weight vinylidenechloride, and

(4) Removing water from the barrier-coated film.

I have found that the particular type of nylon which is obtained frompolycondensation of caprolactam and which is known as and hereafterreferred to as nylon 6 is preferred for use as the substrate filmbecause of its excellent thermoformability and resistance to abrasion.However, the deposition of a barrier coating from a water dispersiononto a nylon 6 substrate presents the problem that the substratewrinkles when contacted with water.

The present invention provides two specific embodiments of the abovenovel process by which to overcome the problem of such wrinkling. Thefirst such embodiment comprises the steps of:

(1) Gravure roll coating a nylon 6 substrate film with a solution ofpolyurethane primer in an organic solvent,

(2) Removing organic solvent from the primer-coated substrate film,

(3) Gravure roll or size press coating the primercoated film with awaterproof coating of a solution of about 7095% vinylidene chloride andabout 530% by weight acrylonitrile,

(4) Removing organic solvent from the waterproof coated film,

(5) Metering bar coating the waterproof coated film with a barriercoating of a water dispersion of a copolymer of vinylidene chloridecontaining about 88% to about 96% by weight vinylidene chloride, and

(6) Removing water from the barrier coated film.

The deposition of a waterproof coating on the primed nylon 6 substrateis sufficient to protect the nylon 6 from the water in the barriercoating dispersion, thus preventing wrinkling of the film.

The specific embodiment of the novel film which is produced by thisprocess comprises a nylon 6 substrate film, a polyurethane primercoating on said substrate film, a waterproof coating of a copolymer ofabout 70- 95% by weight vinylidene chloride and about 5-30%acrylonitrile, and a barrier coating of a copolymer of vinylidenechloride on said waterproof coating, the barrier coating copolymercontaining vinylidene chloride in the amount of about 88 to about 96% byweight. The barrier coated film is substantially free of organicsolvent.

In this embodiment of the film the nylon 6 substrate film can be fromabout /2 to about 5 mils in thickness, preferably from about /2 to about2 mils in thickness; the polyurethane primer layer can be from 0.005 toabout 0.05 mil thick, preferably about 0.01 to about 0.02 mil; thewaterproof coating preferably contains about 90% by weight vinylidenechloride and 10-25% acrylonitrile, can range from about 0.01 to about0.05 mil thick, preferably from about 0.05 mil thick, preferably fromabout 0.01 to 0.03 mil, and is deposited from solution in acetone,toluene or methyl ethyl ketone; and the barrier coating preferably is acopolymer of vinylidene chloride, acrylonitrile, and methyl acrylatecontaining from about 90% to about by weight vinylidene chloride and canrange from about 0.08 to about 0.32 mil thick, preferably from 0.08 toabout 0.16 mil.

The second and preferred specific process embodiment which I havediscovered which overcomes the problem of wrinkling of nylon 6 comprisesthe steps of:

(1) Gravure roll coating a nylon 6 substrate film with a solution ofpolyurethane primer in an organic solvent,

(2) Removing organic solvent from the primer-coated substrate film,

(3) Metering bar coating the primer-coated substrate film with a barriercoating of a water dispersion of a copolymer of vinylidene chloride,said copolymer containing about 88% to about 96% by weight vinylidenechloride,

(4) Removing water from the barrier-coated substrate film, and

Controlling the tension of the film, preferably automatically, duringsteps L4 to prevent wrinkling of the film.

I have found that when the tension of the film during coating iscontrolled, the previously described waterproof coating can be omittedfrom the film without incurring a wrinkling problem.

The specific embodiment of the above-mentioned novel film produced bythis preferred process comprises nylon 6 substrate film, a polyurethaneprimer coating on said substrate film, and a barrier coating of acopolymer of vinylidene chloride containing vinylidene chloride in theamount of about 88% to about 96% by weight. The barrier coated film issubstantially free of organic solvent.

In this embodiment of the film the nylon 6 substrate film can be fromabout /2 to about 5 mils in thickness, preferably about /2 to about 2mils; the polyurethane primer layer can be from about 0.005 to about0.05 mil thick, preferably about 0.01 to about 0.02 mil; and the barriercoating is preferably a copolymer of vinylidene chloride, acrylonitrileand methyl acrylate containing from about 90 to about 95% by weightvinylidene chloride and can range from about 0.08 to about 0.32 milthick, preferably from about 0.08 to about 0.16 mil.

The invention will now be more particularly described with reference tothe drawings in which:

FIG. 1 is a cross-sectional view of the film produced by the firstspecific embodiment of the novel process of this invention.

FIG. 2 is a cross-sectional view of the film produced by the second andpreferred specific embodiment of the process of this invention.

FIG. 3 is a schematic view of the apparatus used in carrying out thefirst specific embodiment of the process of this invention.

FIG. 4 is a schematic view of the apparatus used in carrying out thesecond and preferred specific embodiment of the process of thisinvention.

With respect to FIG. 1, reference numeral 1 indicates the substrate filmof nylon 6. This film can be of /2 to 5 mil thickness and is preferablyof /2 to 2 mil thickness. Reference numeral 2 indicates the polyurethaneprimer coating which can range from about 0.005 to about 0.05 mil thick,preferably about 0.01 to about 0.02. Reference numeral 3 indicates thewaterproof coating of a copolymer of about 70-95% by weight vinylidenechloride and about 530% by weight acrylonitrile. The waterproof coatingcan be of about 0.01 to about 0.05 mil thickness, preferably about 0.01to about 0.03 mil. Reference numeral 4 indicates a barrier coating of acopolymer containing about 88 to about 96% by weight vinylidenechloride, with the remainder consisting of one or more of the followingcomonomers:

methacrylic acid and its alkyl esters, acrylic acid and its alkylesters, acrylonitrile,

methacrylonitrile,

vinyl chloride, and

itaconic acid.

The barrier coating can range from about 0.08 to about 0.32 milthickness, and is preferably from about 0.08 to about 0.16 mil thick.

With respect to FIG. 2, reference numeral 5 indicates the substrate filmof nylon 6 which can be from about /2 to 5 mils thickness, preferablyabout /2 to about 2 mils. Reference numeral 6 indicates the polyurethaneprimer coating which is of about 0.005 to about 0.05 mil thickness,preferably about 0.01 to about 0.02 mil. Reference numeral 7 indicates abarrier coating of a copolymer of vinylidene chloride with one or moreof the comonomers set forth in the previous paragraph. The barriercoating contains about 88% to about 96% by weight vinylidene chlorideand can range from about 0.08 to about 0.32 mil thick, preferably about0.08 to about 0.16 mil. All of the coating thicknesses set forth in thisspecification and in the accompanying claims are dry thicknesses, i.e.thicknesses of the coatings in their finished form after application anddrying.

With respect to FIG. 3, reference numeral 8 indicates the unwind rollfrom which the nylon 6 is fed. Reference numeral 9 indicates thesubstrate film of nylon 6 and will be used hereafter to denote thecoated film in the various stages of this embodiment of the process.Reference numeral 10 indicates a reservoir of primer, said primercomprising a polyester component and an isocyanate-catalyst componentwhich together form a polyurethane. Globe-Hamilton 118-l7 Primer is anexample of the polyester component and Globe-Hamilton 118-18 Catalyst isan example of the isocyanate-catalyst component. Both are made byGlobe/Hamilton Color Works, Inc. of Chicago, Ill. The former is apolyester having approximately the following composition by Weight:

Percent Ethylene glycol 14.3 2,2-dimethyl 1,3-propanediol (neopentylglycol) 19.7 Terephthalic acid 66.0

The latter component is a polyol-tolylene diisocyanate condensationproduct.

Reference numeral 11 indicates a gravure roll which picks up the primerand deposits it on the underside of film 9. Reference numeral 12indicates a doctor blade which serves to scrape excess primer from thegravure roll. Reference numeral 13 denotes the rubber compression rollwhich is used to hold the film 9 against the gravure roll. The gravureroll is driven by a motor which is not shown. The compression roll mayalso be driven if desired. These rolls draw the film from unwind roll 8.Reference numerals 14, 15, 16, 17 and 19 indicate idler rolls, idlerrolls 15, 16 and 17 being located in a first dryer 20 which removessolvent from the primer-coated substrate film. The dryer is ofconventional construction. During its passage through dryer 20 the film9 is preferably carried on a belt 21 which is driven by a drive roll 18.Upon emerging from the dryer the primer-coated film 9 is cooled byconventional means and then passes over idler rolls 22, 23, 24 and 25 toa second coating station composed of a second reservoir 26 filled with asolvent solution of a copolymer of vinylidene chloride andacrylonitrile. The copolymer consists of about 70-95% by Weightvinylidene chloride and about 530% by weight acrylonitrile, for example,Saran F220, marketed by the Dow Chemical Co. of Midland, Mich. Thefunction of this coating is to waterproof the nylon 6 substrate film toprevent its wrinkling due to water sensitivity. The copolymer isreceived as a solid and may be dissolved in acetone for application.Another solvent which can be used is a mixture of toluene and methylethyl ketone. This second coating station also consists of a motordriven gravure roll 27, a doctor blade 28, and a rubber compression roll29 which may be motor driven if desired. These rolls serve to pull thefilm therebetween and operate in the same manner as those of the firstcoating station. I have found that size press coating is also suitableas a method of applying the waterproof coating. By size press coating Imean gravure coating with a smooth surfaced roll. Hereafter in thespecification and claims, when used in conjunction with application ofthe waterproof coating, the terminology gravure roll coating is meant toencompass also size press coating. The waterproof coated film emergesfrom the second coating station and passes over idler rolls 30, 31, 32,and 33 and drive roll 34, of which 31, 32, 33,

and 34 are located in a second dryer 35 which preferably has a belt 36carrying the film in the same manner as the belt of dryer 20. The dryeris of conventional construction and serves to remove organic solventfrom the waterproof-coated film. After passing from dryer 35, the film 9passes over a cooling drum 37 which is maintained at about ambienttemperature, around which it is partially wrapped by roller 38. The filmthen passes over idler rolls 39, 40, 41 and 42 to a third coatingstation, where a reservoir 43 contains a water dispersion of a barriercoating of a copolymer of vinylidene chloride with one or more of thefollowing comonomers:

methacrylic acid and its alkyl esters, acrylic acid and its alkylesters, acrylonitrile,

methacrylonitrile,

vinyl chloride, and

itaconic acid.

The barrier-coating copolymer is about 88-96% by weight vinylidenechloride, preferably 90-95%. The preferred barrier coating copolymer iscomposed of vinylidene chloride, acrylonitrile and methyl acrylate. Whenthe barrier coating copolymer contains below 88% vinylidene chloride thecoated film does not present a satisfactory barrier coating (i.e. itpasses more than 1 cc./ 100 in. 24 hoursatmosphere); when the barriercoating copolymer contains above 96% vinylidene chloride the barriercoating on the film is too brittle to be satisfactorily used. Thebarrier coating copolymer may be, for example, Daran 210, marketed byDewey and Almy Division of W. .R. Grace & Co., Cambridge, Mass. Asmooth-surfaced driven roller 44 picks up barrier coating from reservoir43 and deposits it on the underside of the film 9. The film then passesover a metering bar 45 which consists of a wire-wound rod. This meteringbar serves to scrape excess barrier coating from the coated film in sucha way as to assure a uniform coating which will yield a coat of thedesired dry thickness. More than one metering bar can be used ifdesired.

I have found that a conventional air knife can be used, if desired,instead of or together with the wire-wound rod for scraping away excesscoating. The terminology metering bar coating when used hereafter in thespecification and claims is meant to encompass smooth roll coating thefilm and scraping away the excess coating with either a wire-wound rod,an air knife, or a combination thereof.

After emerging from the third coating station, the barrier coated filmpasses over rubber covered driven roll 46, idler rolls 47, 48 and 49 anddrive roll 50, of which 47, 48, 49 and 50 are located in third dryer 51.Dryer 51 is of conventional construction and serves to remove Water fromthe barrier coated film. Again the film is preferably carried throughthe dryer on a belt 50'. After emerging from dryer 51, the coated filmpasses over a cooling drum 52 which is maintained at about ambienttemperature and then over roll 53 positioned immediately adjacentthereto in such a manner as to cause the film to wrap partially aroundcooling roll 52. After passing over roll 53 the cooled coated filmpasses over an idler roll 54 and onto a rewind spool 55.

In summary, the substrate nylon 6 film has been coated with a primerwhich serves to bond a subsequent waterproof coating thereto, whichwaterproof coating serves to protect the nylon film from the water in asubsequent barrier coating.

Although the primer and waterproof coatings are applied from solution inorganic solvent, they give rise to no odor and taste problems in theproduct film because the thinness of these coatings allows the organicsolvents to be substantially completely removed during the drying steps.

FIG. 4 is a schematic view of apparatus for carrying out the second andpreferred specific embodiment of the process of this invention. Nylon 6substrate film is fed from an unwind roll and passes over idler rolls101 and 102 and then over a brake controlling roll 103. This roll isequipped with a feedback system which sends a signal to a brakingapparatus on unwind roll 100, as indicated by arrows 103'. The lower thetension in the film at 103, the more braking which results at 100 andvice versa. In this manner a smooth, taut feed-sheet of substrate filmis assured. The film 104 then passes over the main drive roll 105, overidler rolls 106 and 107 and a first tension sensing roll 108. Afterpassing over roll 108 the film passes over a conventional bowed roll 109which exerts a transverse stretching effect on the film. This stretchingeffect, while insuificient to distort the film, is suflicient to insurewrinkle-free feed.

The film then passes through a first coating station composed of areservoir 110, containing a polyurethane primer of the type previouslydescribed, a motor driven gravure roll 111, a doctor blade 112 and arubber compression roll 113 which may be motor driven if desired. Thegravure roll 111 is so positioned as to dip into reservoir 110. Therolls 111 and 113 rotate in the direction of travel of the film thusdrawing the film between them and the film is pressed against thegravure roll 111 by the rubber compression roll 113. As gravure roll 111dips into the primer and rotates to contact the film, any excess primeris removed from the roll by the use of doctor blade 112 which scrapesexcess material from the roll. Thus, even coating of the primer isdeposited on the nylon 6 substrate film 104. The speed of the motorsdriving rolls 111 and 113 is variable and is adjusted automatically bymeans of a signal fed forward to variable speed drive means as indicatedby arrows 108, from first tension sensing roll 108 so as to maintainproper tension in the film between the main drive roll and the nipformed by the rolls 111 and 113. The means by which the speed adjustingsignal is transmitted and received is conventional pneumatic, electricor hydraulic automatic control equipment which may include an amplifier;however, since such equipment is conventional the details of thecircuits have not been shown.

After passing through the nip the film passes over an idler roll 114 andover second tension sensing roll 115. The film and the rolls are sopositioned that only the dry side of the film contacts the rolls, forobvious reasons. After passing over second tension sensing roll 115 thefilm enters a first dryer 116 wherein it passes over a series of idlerrolls, for example 118, and wherein the organic solvent is removed fromthe primer coated film. The film, when in the dryer, is preferablycarried on a belt 117 which is driven by drive roll 118'. After emergingfrom first hot-air dryer 116, the film passes over a drive roll 119.Drive roll 119 is driven by variable speed drive means at a speedresponsive to a signal, indicated by arrows 115 fed from second tensionsensing roll 115 through conventional automatic control equipment, thusmaintaining the proper degree of tension in the film while it passesthrough bot-air dryer 116. Belt drive roll 118' is preferablyinterconnected with drive roll 119 so as to be driven at a slightlyslower speed than 119. If desired, signal 115' may be fed directly tovariable speed drive means on roll 118'.

After passing over drive roll 119, the film 104 passes over cooling drum120 which is maintained at about ambient temperature. The cooling drum1-20 is positioned in such a manner with respect to drive roll 119 andad jacent roll 121 as to require the film to wrap around a major portionof cooling drum 120. If desired, more than one cooling drum can be used,or drive roll 119 can be, in addition, a cooling drum. After passingover idler roll 121 the cooled primer-coated film 104 passes overadditional idler rolls such as 122, and then over third tension sensingroll 123 and bowed roll 124 and beneath an idler roll 125 which forcesthe film against a smoothsurfaced applicator roll 126. The applicatorroll 126 transfers a barrier coating, previously described with respectto FIG. 2, from a reservoir 127 onto the underside of film 104. Awire-wound metering bar 128 of the type previously described is used tometer the amount of barrier coating applied to film 104. This meteringbar serves to scrape the coated film in such a way as to assure auniform coating of the desired thickness. More than one metering bar canbe used if desired.

I have found that a conventional air knife can be used, if desired,instead of or together with the wire-wound rod for scraping away excesscoating. The terminology metering bar coating when used hereafter in thespecification and claims is meant to encompass smooth roll coating thefilm and scraping away the excess coating with either a wire-wound rod,an air knife, or a combination thereof.

After passing over driven rotating metering bar 128 the barrier coatedfilm 104 passes over a drive roll 129 which is driven by variable speeddrive means at a speed controlled by a signal 123' fed forward fromthird tension sensing roll 123 through conventional automatic controlequipment. The film then passes over fourth tension sensing roll 130 andthen into a second dryer 131 where it passes over a series of idlerrolls, for example 132. The film, when in the dryer is preferablycarried on a belt 133 which is driven by drive roll 132'. Drive roll134, positioned adjacent the exit from dryer 131, is driven at a speedresponsive to a signal, indicated by arrows 130, fed from fourth tensionsensing roll 130 thus maintaining the proper degree of tension in thefilm while it passes through the hot-air dryer. Belt drive roll 132' ispreferably interconnected with drive roll 134 so as to be driven at aslightly slower speed than 134. If desired, signal 130 may be feddirectly to variable speed drive means on roll 132'.

After passing over drive roll 134, the film passes over a cooling drum135 which is maintained at about ambient temperature. If desired, morethan one cooling drum can be used, or drive roll 134 can itself be acooling drum. The cooled, primer coated film 104 then passes overadditional idler rolls such as 136, 136', 137 and 137 and over anadditional tension sensing roll 138. The film then passes through a setof conventional divergent nip rolls 139 which exert a transversestretching force on the film to a degree sufiicient to prevent wrinkleformation but not sufiicient to permanently stretch the film. The filmthen passes onto a rewind spool 140 which is driven by a variable speedmotor at a speed responsive to a signal 138' fed from tension sensingroll 138, by means of conventional automatic control equipment, so as tomaintain a proper degree of tension in the film.

I have found that the tension in the film during the above processshould be maintained at about 0.25% to 40%, preferably 25%, of the yieldpoint of the film being used, when the yield point is expressed inlbs./in. By yield point I mean the first point on a stress-strain curvefor the fihn at which strain increases without increase in stress. Theyield point is normally expressed in pounds per square inch. In order toexpress it in pounds per inch the yield point in lbs./sq. in. ismultiplied by the thickness of the film in inches. AST M SpecificationD882-6l2T was used in determining the stressstrain curve of the film.

By means of this second specific embodiment of the process of thisinvention it is possible, by controlling tension in the film, preferablyautomatically, to eliminate the waterproof coating and dryer thereforused in the first specific embodiment of the process with consequentsavings in cost. For this reason the second specific embodiment of theprocess is the preferred embodiment.

The following table shows a comparison of the properties of severalsamples of the barrier coated film made by the first specific embodimentof the process of this invention with the properties of several samplesof barrier-coated 50M25 Mylar packaging film (Mylar is a trademark forpolyethyleneterephthalate film). The barrier coating copolymer used onthe nylon 6 film consisted of about by weight vinylidene chloride withmethyl acrylate and acrylonitrile:

Barrier coated film Property Mylar Nylon 6 0: transmission rate, ec./in. -atm.-24 hrs- 1. 0 1. 0 Adhesion 1 Passed 1 Passed Odor 6. 4 7. 2-8.8 Taste 6. 2 8. 8-10 Retained solvent, percent Trace 0. 05 Wrinkl NoneNone 4. 7 3. 1-4. 6

1 Ambient conditions; scored specimen.

Barrier coated film Property Mylar Nylon 6 Oxygen transmission rate,ee./100 in. -atm.-

24 hrs 0. 5-0. 9 0. 5-0. 9

2 Passed 2 Passed 3 Trace 3 Trace None None 2 Specimen scored and testedafter aging 16 hours at 100% relative humidity.

* 100 p.p.m.

The above tables show that the barrier coated nylon 6 films of bothspecific embodiments of the process of this invention are eithercomparable to or superior to barrier coated Mylar films in each of theabove properties. The data shows superiority in the properties of odor,taste, haze and gloss. Barrier coated Mylar was used in the above tablesfor comparison purposes due to its wide acceptance in the packagingindustry for packaging such things as lunch meats.

Although barrier coated film has been defined herein as meaning abarrier to oxygen, the barrier coated films of this invention alsoexhibit good barrier properties with respect to gases such as watervapor, CO and nitrogen.

Before use as a packaging material the barrier coated films of thisinvention are preferably laminated to polyethylene film by aconventional laminating process utilizing an adhesive. Alternatively thepolyethylene can be applied by extrusion coating. The barrier coatedfilms are preferably laminated to or coated with polyethylene before useas a packaging material chiefly because of the superior heat-sealabilitywhich the polyethylene provides. The resulting laminate thusincorporates the best features of its two components, i.e. the superioroxygenbarrier properties of the barrier coated nylon 6 and the superiorheat scalability of polyethylene.

Laminates of the films of this invention and of barrier coated Mylar,made by laminating these fihns to polyethylene, were compared by vacuumpackaging lunch meat samples (bologna and hot dogs) therein by heatsealing, and aging the samples under extreme shelf-life conditions (38F., 50-70% relative humidity and foot candles of light with lights on 24hours per day). The barrier coated nylon 6 laminates were found to beequivalent in shelf life to the barrier coated Mylar laminates, bothhaving a shelf-life (the length of time before the packaged meatdiscolored) of more than 10-14 days.

9 Barrier coated nylon 6 laminates were found to be superior in thatthey could be formed (by drawing) into deep containers (for example, 1/2" to 1%) with less incidence of ruptured containers than the barriercoated Mylar laminates.

In addition to providing a superior packaging material for lunch meatsand cheeses, the films of this invention have been found to provide asuperior packaging material for frozen vacuum packaged meats, due totheir ability to withstand the tensile stresses at low temperaturecaused by expansion of meats on freezing, and the abrasion and flexingcaused by handling at low temperatures.

The manner of testing of each of the various properties of the film setforth in the above tables is described in the paragraphs below.

TRANSMISSION RATE The film sample to be tested was mounted in avolumetric gas transmission cell (maintained at 73 F.) so as to form abarrier between the two chambers of the cell. The first chamber waspressurized to 50 p.s.i.g. with oxygen. The second chamber, which wasmaintained at atmospheric pressure, was connected to a glass capillarycontaining a short column of liquid whose movement measured the changein gas volume in the second chamber due to the passage of gas throughthe film sample during the test. The resultant volume change wasconverted into the units of cc./ 1.00 in. of film surface24 hrs.,elapsed time--atmosphere of imposed pressure. An oxygen transmissionrate of 1.0 cc./ 100 in. -24 hrs.-atmosphere or less is considerednecessary by the packaging industry in order to assure reasonableshelf-life of lunch meats and cheeses.

ADHESION The Scotch Tape test was used, since it is the standard type ofadhesion test used in the film coating industry. Scotch brand cellophanetape (No. 610) was applied to the surface to be tested and then pulledfrom the tested surface and examined. If the tape had lost its tackinessdue to adhered coating or the tested surface showed signs of peeling,the test was a failure. Several modifications of this test were used,some of which are outlined below:

(a) Ambient conditions:

Sample scored (lightly scratching a grid pattern on the coated surfacewith a razor blade), tape applied and removed slowly.

Sample scored, tape applied and removed with a rapid jerking motion.

Same as the above two tests but without scoring the sample.

(b) After aging at 140 F., sixteen hours, and 100% relative humidity,the same tests as set forth above.

ODOR

The odor test of the National Flexible Packaging Association was used.This test uses a scale of -10 with indicating no odor.

TASTE The taste test of the National Flexible Packaging Association wasused. This test uses a scale of from 0-10 with a value of 10 indicatingno taste.

RETAINED SOLVENT A 2-ft. piece of film was inserted in a one-liter flaskwith a threaded neck. The top of the flask was sealed with aluminum foiland tape and then the cap was screwed on. The flask was heated in anoven at 60 C. for an hour. The flask was removed and cooled at roomtemperature and the cap removed. A Q ml. sample of the air in the flaskwas taken by inserting a hypodermic needles through the foil and pumpingthe plunger several times. The sample was analyzed for retained solventin a gas chromatograph.

WRINKLES This was a subjective test done by visual examination.

HAZE

Haze measurements were made using ASTM test D1003-61. Results areexpressed in percent of light failing to pass through the film due tohaze. Thus, the lower the value, the less haze present.

GLOSS Gloss was measured by the use of a Gardner Gloss meter at a 20angle. The value indicates the reflectance of the film. The higher thevalue, the glossier the film.

While the invention has been described with particular reference tospecific embodiments, it is to be understood that it is not to belimited thereto but is to be construed broadly.

I claim:

1. A plastic film, substantially free of organic solvent, comprising:

(a) a nylon substrate film,

(b) a polyurethane primer coating on said substrate film, and

(c) a barrier coating overlying said primer coating,

said barrier coating consisting of a copolymer of vinylidene chloridewith at least one comonomer selected from the group consisting of:

methacrylic acid and its alkyl esters, acrylic acid andits alkyl esters,acrylonitrile, methacrylonitrile, vinyl chloride, and itaconic acid, thecopolymer containing about 88% to about 96% by weight vinylidenechloride.

2. The film of claim 1 wherein the alkyl esters of methacrylic andacrylic acid are those having an alkyl group containing 1-8 carbonatoms.

3. A plastic film, substantially free of organic solvent, comprising:

(a) a poly(e-caprolactam) substance film,

(b) a polyurethane primer coating on said substrate (c) a waterproofcoating on said primer coating, said Waterproof coating consistingessentially of a copolymer of about 70-95% by weight vinylidene chlorideand about 530% by weight acrylonitrile, and

(d) a barrier coating on said waterproof coating, said barrier coatingconsisting of a copolymer of vinylidene chloride with at least onecomonomer selected from the group consisting of:

methacrylic acid and its alkyl esters, acrylic acid and its alkylesters, acrylonitrile, methacrylonitrile, vinyl chloride, and itaconicacid, the copolymer containing about 88% to about 96% by weightvinylidene chloride.

4. The film of claim 3 wherein the alkyl esters of methacrylic andacrylic acid are those having an alkyl group containing 1-8 carbonatoms.

5. The film of claim 4 wherein vinylidene chloride is present in saidbarrier coating copolymer in the amount of about 90% to about by weightand the comonomers are methyl acrylate and acrylonitrile.

6. The of claim 5 wherein said poly(e-caprolactam) substrate film isfrom about /2 to about 5 mils thick, said polyurethane coating is fromabout 0.005 to about 0.05 mil thick, said waterproof coating is fromabout 0.01 to about 0.05 mil thick and said barrier coating is fromabout 0.08 to about 0.32 mil thick.

7. The film of claim 6 wherein said poly(e-caprolactam) substrate filmis from about /2 to about 2 mils thick, said polyurethane primer coatingis from about 0.01 to about 0.02 mil thick, said waterproof coating isfrom about 0.01 to about 0.03 mil thick and said barrier coating is fromabout 0.08 to about 0.16 mil thick.

8. The film of claim 7 wherein said film is laminated to polyethylenefilm.

9. A plastic film, substantially free of organic solvent comprising:

(a) a poly(e-caprolactam) substrate film,

(b) a polyurethane primer coating on said substrate film, and

(c) a barrier coating on said primer coating, said barrier coatingconsisting of a copolymer of vinylidene chloride with at least onecomonomer selected from the group consisting of:

methacrylic acid and its alkyl esters, acrylic acid and its alkylesters, acrylonitrile, met-hacrylonitrile, vinyl chloride, and itaconicacid,

the copolymer containing about 88% to about 96% by weight vinylidenechloride.

10. The film of claim 9 wherein the alkyl esters of methacrylic andacrylic acid are those having an alkyl group containing 1-8 carbonatoms.

11. The film of claim 10 wherein vinylidene chloride is present in saidcopolymer in the amount of about 90% to about 95% by weight and thecomonomers are methyl acrylate and acrylonitrile.

12. The film of claim 11 wherein said nylon substrate film is from about/2 to about mils thick, said polyure- 12 thane coating is from about0.005 to about 0.05 mil thick, and said barrier coating is from about0.08 to about 0.32 mil thick.

13. The film of claim 12 wherein said nylon substrate film is about /2to about 2 mils thick, said polyurethane primer coating is from about0.01 to about 0.02 mil thick and said barrier coating is from about 0.08to about 0.16 mil thick.

14. The film of claim 13 wherein said film is laminated to polyethylenefilm.

References Cited UNITED STATES PATENTS 4/ 1961 Spencer et a1. 1/1967Maschner et a1 161-190 US. Cl. X.R.

